Internal combustion engines of the diesel type are an essential part of the automotive and agriculture industries. The fundamental diesel process depends upon the heat of compression to ignite an air fuel mixture where fuel has been injected at or near top dead center during the compression stroke of the engine. Over the years, a wide variety of systems have been proposed and adopted to achieve the end of a predetermined quantity of fuel under high pressure at a predetermined time in the engine cycle to achieve the necessary performance and emission goals for the diesel engine. These fuel systems include high pressure common rail systems (HPCR), unit injectors, distributor systems, and multiple unit injector pump systems. One of the common requirements of all such systems is the ability to have a solid column of fuel from a fuel supply to the fuel injection system, i.e. no trapped air in the fuel supply. This is necessary to provide the correct quantity and timing of injected fuel but also to lubricate the close tolerance moving parts of the fuel injection system.
To this end, it is necessary to rapidly fill the line from a fuel supply to the fuel injection system prior to engine startup so that initial operation is on the basis of a solid column of fuel in the system. At the same time, the fuel supply to the fuel injection system must not be above certain flow levels during engine operation since most fuel injection systems have a return flow feature for fuel that is not consumed by the engine. The process of pressurizing fuel for delivery to the combustion chambers of an engine produces heat which is transferred to the fuel. Any fuel, not consumed by the engine, goes back to the fuel tank. In the event of an excess of fuel passing to the fuel injection system, the heat input to the fuel can be significant and require fuel coolers to avoid the adverse consequences of fuel that has been heated to a significant temperature.
In no system is the requirement for a solid column of fuel more important than in the class of fuel system comprising unit injectors in which the injection pressure is derived from a cam actuated plunger to achieve ultra high injection pressures. In such a system, a common inlet passage or chamber is positioned adjacent each of the injectors and solenoid valves control the timing and quantity of fuel admitted to each of the plungers for injection into the engine combustion chamber. Such a system has a pressure adjacent the injectors at a level about 100 psi. Under some conditions, after shut down of the engine, air can enter into the system so that it is possible to have fuel/air or air entering the injection chamber which has an adverse affect on engine performance.
Accordingly, there exists a need in the internal combustion engine art for a fuel system that minimizes, if not eliminates aeration of the fuel but limits return flow under engine operating conditions. Furthermore there exists a need in the art for a simplified unitary valve accomplishing these functions.